The two heads of Microsoft are finding themselves on opposite sides of a battle in Washington State over the imposition of a state income tax that would apply to only upper-income earners.

Microsoft founder and chairman Bill Gates and his father William Gates Sr. are supporting Initiative 1098, set to appear on the November ballot. If the initiative passes, a 5 percent tax would be levied on couples who make more than $400,000 or individuals who make more than $200,000, and a 9 percent tax on couples who make more than $1 million or individuals who make more than $500,000. Gates Sr. has even contributed $500,000 to a campaign in support of passing the ballot initiative.

On the opposite side is Microsoft CEO Steve Ballmer, who has contributed $100,000 to the Defeat-1098 campaign, according to The company too is on a list of employers who are officially opposed to the tax, according to the Defeat-1098 campaign. Ballmer is joined by Amazon CEO Jeff Bezos, who has also given $100,000 to defeat the ballot initiative. Opponents argue that the lack of a statewide income tax is one of the selling points of Washington State and that it would be hard to attract more companies to the state with such a tax. However, Washington State, like most states around the country these days, is struggling to close its budget gap.

This may be the first time Gates and Ballmer find themselves in opposite camps, at least publicly. But it doesn’t mean we’re likely to find one of them switching to a Mac anytime soon.